1. FIELD OF THE INVENTION
The present invention relates to the elongated hand piece of a dental instrument or 3-way syringe/water and air regulator having means to prevent contamination of the inside of the elongated hand piece.
2. DESCRIPTION OF RELATED ART
A dental instrument or 3-way syringe/water and air regulator is used by putting its tool in the mouth of a patient to cut or grind selected teeth, and therefore, the end of the instrument is most likely contaminated with blood or saliva, which is liable to invade the inside of the elongated hand piece. Even if the outer surface of the instrument is sanitized, blood, saliva or other impurities remain inside, and therefore the instrument cannot be completely sanitized. If the inside-contaminated instrument is used in the mouth of another patient, such impurities may be released, and therefore, there is a fear of patients being infected with different diseases through the agency of inside-contaminated dental instruments.
There is a strong demand for preventing infection through the agency of inside-contaminated dental instruments by removing blood, saliva or other impurities from the inside of dental instruments. Japanese Utility Model 3-46743(B) discloses an inside contamination-free dental instrument whose elongated hand piece has an air turbine driven by compressed air. The air turbine is rotatably mounted in an associated head casing with the aid of upper and lower bearings, and the head casing has upper and lower lids. Annular slots and annular air cells are formed in the inside of the head casing particularly in the vicinity of the apertures of the upper and lower lids through which apertures the shaft of the air turbine extends, and an air feeding passage communicates with the annular slots and annular air cells. In use air is made to flow in the air feeding passage, allowing air to flow through the annular gaps between the shaft of the air turbine and the circumference of the aperture of each of the upper and lower lids while keeping the inside of the head casing at an increased pressure, thus preventing invasion of blood, saliva or other impurities from the exterior.
Karman's vortex street, however, is liable to appear in the air flow, particularly in the annular slot and annular cell, thereby causing a counter air flow in the annular gaps around the shaft of the air turbine in the upper and lower lids, thus introducing air inside.
As a result, blood, saliva and other impurities in a patient's mouth are liable to be air-borne to the inside of the
dental instrument, and these impurities attach on the annular slots and cells. As a result bacilli will increase within the dental instrument, and then the inside of the dental instrument will be contaminated with such bacilli.